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Monday, July 26, 2010

Audiophile Buzzwords, a dicey subject

How can loudspeaker measurements tell us anything about how a speaker sounds? Audiophiles generally don't think in terms of Polar Response, Impulse Response, Power Compression, etc...

They tend to look at things in subjective terms and often confuse musical terminology, Pace, Rhythm, Timing, Sound Stage, Dynamics, Spaciousness, etc.. for engineering possibilities and vernacular. This is a crude attempt by an amateur, myself, to bring these 2 worlds together. I won't go through all the buzzwords, just a couple to make my point.

Tonality can be looked at from many different metrics, but basically a polar response and impulse response will tell you what you need to know. Some people would argue for phase as well, but the science refutes that claim.

and you'll realize this is a music term, not a playback term. That said, wild polar responses will not have good tonality unless they somehow match the inaccuracies of the recording process--fat chance. If it does on one, it won't on any other. The recording process has as much to do with this as the playback. That's part of the reason why getting a polar response on a speaker is more useful than going and listening to your few favorite tracks. Rise time and Decay should also play a part and can be seen by looking at the impulse graph, CSD, wavelet, etc... With the impulse(s) and a polar plot, you'll have all that info.

What most people seem to describe as soundstage as far as I know mostly has to do with speaker placement and polar response. If you are shooting an even sound across your room and your room and your speakers are placed with the left on the left and the right on the right, away from the walls toed in, I can't see where you could go wrong. A narrow directivity should give you a better image where a wider, a better sense of space.

Spatiousness is another one of those touchy definitions. To me that's mostly reflection above the modal region (search for "Haas Effect" and the "psychoacoustics" post on this blog http://dtmblabber.blogspot.com/2010/12/psychoacoustics.html) and low level detail resolution if you're talking about what's actually contained in the recording. IOW if you want to hear the recording environment as picked up by the microphone and diluted or enhances through the process of production. Which means anything that interferes with that can have an impact. So from the loudspeaker standpoint, impulse, cabinet accelerometer CSD, now it even looks like capacitor vibration(so there may well be credence to more tweaks like God forbid, cables! Nothing has turned up there yet that I know of), and polar response will play into everything. In Dr. Toole's book there are studies that show wider dispersion adds to a sense of spaciousness. It seems rather intuitive. Also contralateral reflections play a role and subsequent elevations in IACC factor in. There are many things that can effect the low level resolution. I'd bet to some degree you can trace this all the way back to the source. This may be the most expensive, difficult and time consuming part to get to the "N"th degree. The room itself is also a large part of this.

Transient response is another one of those CSD, Wavelet, Impulse, polar. It's just rise time and decay. A CSD or Wavelet don't tell us a whole lot without the impulse response--ever really that I can think of.

Dynamics is another interesting topic that depends on wether you are talking physical or psychophysical. The best way to look at this graphically would go back to everything mentioned for transients, then also thermal capacity, power compression and efficiency.

I know, no publisher of specs is giving you this information, so knowing how to use it or think of it is of little use. In the end we are all left to guess. I wonder if informed guessing is better than uninformed. I bet anyone schooled in the issues at hand could do much better than I. Every time I read something new, I learn more and I'm betting any recording engineer, acoustician, transducer engineer, etc... could do a much better job than I just did.

7 comments:

I cringe when I see mention of rhythm, pace and timing. I wish people would keep those kinds of terms for music. Still, I think we also need some subjective terms if we are going to talk about the things we hear. Terms like spaciousness, sound stage and imaging I can live with. I'm not fussed what subjective words people use, as long as I know what they mean. When people start talking about rhythm, I wonder what a CD player could possibly to to alter that without being seriously faulty!

Polar and impulse response tells all? If that's true then you are very easy to please! That might be simplifying things a little too far. I think you will find there are many measurements that will show audible issues, not simply those two. Waterfall plots can be quite revealing regarding in-room bass. Add bass traps and you will see that the faster decay is very audibly different, even where the response is pretty close.

Don't get me wrong - I agree polar plots are one of the first things you want to see, but I'm interested in a great deal more than that.

Thanks Paul! I absolutely respect and appreciate your commentary. I've been reading you site and posts for a long time.

My point about the impulse graph is that all the CSD and wavelet type things are just another way of looking at the impulse. Check out the rest of this blog and you'll see that I use other views of the impulse often, but the more experience I've gained, the more I realize that all you need with regard to the loudspeaker can be seen in the frequency response(anechoic, but gated will do) and the impulse. W/o the impulse, CSD, Spectrogram, etc... can be misleading. That was sort of my point b/c the beam width of a transducer can get reflections into those(if not anechoic) other graphs and cause interpretation errors when if you don't have the impulse. In addition to the impulse they(CSD, Wavelet, etc...) can certainly clarify though I'm not much of a fan of CSD in general. From a psychoacoustics standpoint, a wavelet is more useful. I believe I go into this in my 'gating loudspeaker graphs' entry.

I wasn't really trying to go into "in room" issues as things change there. This was intended to be more of a 'how to' buy a good sounding loudspeaker based on measurements--preferably anechoic. Buying speakers is tough if you are any sort of perfectionist. If you are reading this, you are some sort of perfectionist. ;) We've all read Dr. Olive's "Dishonesty of Sighted Listening" so measurements are the only honest way to go about it. If we went into the psychology of his blog entry, we'd really undestand that he is exactly correct. We are not above sight bias. Look at the McGurk Effect.

Bass has to be measured in room and in the listening position or preferably listening area. So basically we totally agree just I was trying to avoid getting into the room. I do some of that in more recent posts.

Again, thanks for thoughtful commentary. I've deleting many vicious posts from some passionate audiophiles regarding this entry. I deleted my first post of this to clarify a bit.

It's just a frequency response graph taken at several angles and overlaid so that a more relevant view of the sound being put into your listening space can be seen. You essentially want a smooth set of off axis graphs b/c you will hear their reflections and eventual decay when you listen to your loudspeakers. I take mine in 11.25 degree increments from 0-90 degrees.

You write, "A narrow directivity should give you a better image where a wider, a better sense of space."

Ah! So if a speaker has a "big soundstage", that means it is a less directional speaker, right? In which case it seems like "imaging" and "soundstage" work against each other, since to get more of one you would have to give up some of the other(?).

OK, I've thought about this a bit. The problem is that there is not set definition for the subjective terms and often they are used interchangeably. That said, I think what you are asking is typically true, but if narrow directivity speakers are cross-fired they take on an amazingly spacious character. Narrow directivity will also have advantages in SBIR(though not necessarily where it is useful) and Initial Time Delay (something I haven't blogged about) problems so they should retain their imaging while cross-fired.